A vacuum chamber is an element of charged particle accelerators of commercial type used, for example, for chemical and radiation treatment of materials and is intended to extract the beam of charged particles formed by the accelerator into an atmosphere. The beam passes through an exit window of the vacuum chamber, made of thin metal foil, which separates the vacuum volume of the accelerator from the atmospheric pressure.
Known to the prior art is a vacuum chamber (cf. U.S. Pat. No. 3,778,655 published in 1973), wherein the foil is fixed between a vacuum chamber flange and a clamping flange by screws spaced along the periphery of the foil.
Replacing of the foil in the course of operation is a complicated time-taking process, since the foil is fixed simultaneously with mounting of the clamping flange, and because assembling of the unit is performed in a tight room limited by pipelines of a watercooling system of the chamber and a conveyor, transferring products to be irradiated. Moreover, fixation of the foil in the chamber may prove to be not sufficiently vacuum-tight.
Also known is a charged particle accelerator vacuum chamber, described in a dissertation work by G. S. Krainov "Uskoritel electronov dla pricladnych tselei (constructsia i raschot)", Novosibirsk, 1975. The exit window of this vacuum chamber represents a frame with a foil and a flange, to which the frame is secured. The frame consists of two flanges screwed together with a foil therebetween fixed in a vacuum-tight manner. This frame is connected to the flange of the vacuum chamber through a gasket by screws, spaced along the periphery of the window, as in the above-described vacuum chamber.
Replacing the foil of the exit window in such a vacuum chamber is performed by replacing the frame, which is assembled and leakage tested previously and not on the accelerator, but on a special working place, this being undoubtedly much more convenient as compared to the fixing operation of the foil in the vacuum chamber according to U.S. Pat. No. 3,778,655. Moreover, a more reliable vacuum seal between the foil and the chamber is gained. However, the replacing of the frame in this vacuum chamber is still a labour-consuming operation, requiring to unscrew completely all screws fastening the frame to the flange and then to tighten them again, the number of the screws, assuming the length of the exit window to be 1 meter, being from 30 to 50. Further, to achieve a leakage-tight connection of the foil to the vacuum chamber, the frame should be sufficiently bulky, this also being a problem in mounting the frame within a limited room.
Besides, the design of the vaccum chamber is rather complicated since a second vacuum seal and a second set of screws is added.